Multilobal hollow filaments having stiffening ribs and stiffening webs

ABSTRACT

The present invention relates to a multi-lobal hollow filament having stiffening ribs in the core portion and at least one transverse web in each lobe.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multi-lobal hollow filament havingstiffening ribs in the core portion and at least one transverse web ineach lobe, and to a spinneret plate for producing the filament.

2. Description of the Prior Art

Fibers useful for carpet manufacture exhibit certain desirableperformance criteria. These criteria include good crush resistance, highcover and good soil hiding ability. The structure of the fiber is adeterminative factor in the ability of a given fiber to meet theseperformance criteria.

The crush resistance of a carpet depends on the stability properties ofthe pile fibers used in the carpet. The higher the stability of thefiber, the more resistant to crushing is the carpet. The coveringability of a carpet is determined by the space occupied by the fibercross-section. For a given crimp a measure of the space occupancy for alobal fiber is given by the fiber's modification ratio. The higher themodification ratio of the fiber, the greater the covering ability of thecarpet.

The presence of hollow regions in the interior of the fiber furtherincreases the covering power and simultaneously increases its lightscattering ability and decreases its luster. Thus, the presence ofhollow regions coupled with the modification ratio, determine thefiber's covering and soil hiding ability. U.S. Pat. No. 5,380,592 (Tung)and European Patent Office Publication 661,391 disclose a trilobal ortetralobal filament having a hollow core portion and an axiallyextending void in each lobe.

In another aspect hollow fibers with the same modification ratio andsurface area as against solid fibers reduce the specific gravityaccording to the percentage of the fiber that is hollow. For example, atwenty percent hollow (or “void”) ratio reduces the specific gravity ordensity for nylon fibers from 1.14 to 0.91 grams per cubic centimeterand reduces the specific gravity for polyester fibers from 1.35 to 1.08grams per cubic centimeter (both twenty percent reductions). This isdesirable for lightweight carpets, apparel or fabrics.

Designing the structure of the fiber to enhance one of these performancecriteria is often detrimental to another performance criterion. Forexample, in U.S. Pat. No. 5,208,107 (Yeh et al.), a multi-lobalsynthetic fiber has a single axially extending central void. Althoughthis structure may enhance the fiber's stability it is not well-suitedto enhance the soil hiding ability of the fiber.

As another example, U.S. Pat. No. 4,770,938 (Peterson et al.) shows atrilobal fiber having elongated voids extending through each lobe.Although such a structure increases the soil hiding capability of thefiber the lack of rigidity makes the lobes prone to collapse, thusdetracting from the crush resistance of the fiber. If the structure ofthe lobes were rigidified as in U.S. Pat. No. 5,322,736 (Boyle et al.)the fiber becomes more crush resistant, at the cost of increasedpolymer.

In view of the foregoing, it is believed advantageous to provide amulti-lobal fiber structure that optimizes the fiber's soil hiding andcovering ability, without sacrificing crush resistance and withoutincreasing the volume of the polymer material in the fiber.

SUMMARY OF THE INVENTION

The present invention is directed to a thermoplastic synthetic polymerfilament comprising a core portion having a number N lobes joinedthereto. Preferably, three or four. lobes may be provided, therebyrespectively defining trilobal and tetralobal filament configurations.Each lobe has a tip thereon and is joined to the core portion along aninscribing circle. The filament has a central axis extendingtherethrough. N stiffening ribs are formed in the core portion, with theribs extending radially inwardly toward the axis of the filament. Thestiffening ribs cooperate to define at least N hollow regions in thecore portion. Each hollow region in the core aligns radially with arespective lobe.

In one embodiment the radially inner ends of the stiffening ribs may bespaced from each other and from the central axis of the filament,thereby to define passages within the core portion through which thehollow regions communicate with each other. Alternatively, eachstiffening rib may extend to meet and join to the other of the ribsalong the axis of the filament whereby the hollow regions in the coreportion are isolated from each other. The ribs in the core portion formabutting members on the interior of the filament that contact with eachother under high face loading to enhance the stiffness and load capacityof the filament.

Each lobe has at least one opening disposed between the tip of the lobeand the inscribing circle. The opening in each lobe and the hollowregion of the core portion corresponding to that lobe cooperate todefine a transverse stiffening web across each lobe. The presence of thetransverse stiffening web across each lobe prevent the lobe lateraledges from being deformed towards the exterior of the filament,resulting in a high degree of rigidity and crush resistance.

In accordance with another modified embodiment each lobe may be providedwith a second opening therein so that the first and the second openingscooperate to define a second transverse web extending across the lobe.When provided the second opening in each lobe is disposed between thefirst opening and the tip of the lobe.

In yet another embodiment the major portion of each lateral edge of eachlobe may be substantially linear over substantially its entire length.The arm angle for linear edge filament lies in the range from about zeroto about fifteen degrees. Alternatively, the major portion of eachlateral edge is convexly curved over substantially its entire length.

Any filament in accordance with any of the various embodiments of theinvention illustrated herein has a modification ratio that lies in therange from about 1.6 to about 4.0, and preferably in the range fromabout 2.0 to 3.0, and most preferably in the range from about 2.3 toabout 2.6. The filaments have a total void percentage in the range fromabout seven (7%) to about thirty percent (30%), and more preferably, inthe range from about twelve (12%) to about twenty-two percent (22%).

In another aspect the present invention is directed to a spinneret platefor producing any of the thermoplastic synthetic polymer filamentssummarized above. The spinneret plate comprises a cluster of N pairs ofperipheral slot segments centered about a central point. To form lobeshaving substantially linear or convexly curved lateral edges, theperipheral slot segments are either substantially linear or convexlycurved, respectively.

Each peripheral slot segment in each pair is joined to an adjacentperipheral slot segment at a junction point. A rib-forming slot extendsradially inwardly from each junction point toward the central point ofthe cluster. The distance between the junction point and the centralpoint of the cluster occupied by each rib-forming slot determineswhether the ribs meet at the axis or whether the inner ends of the ribsare spaced from the axis.

Each slot segment in each pair is confrontationally disposed withrespect to a slot segment in another pair. At least one web-forming slotextends from each peripheral slot segment toward the peripheral slotsegment with which it is confrontationally disposed. If desired, asecond web-forming slot may also extend from each peripheral slotsegment toward the confrontationally disposed peripheral slot segment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription, taken in connection with the accompanying drawings, whichform a part of this application and in which:

FIG. 1A is a cross section view of a straight-edged trilobal filament inaccordance with the present invention in which each lobe has a singletransverse stiffening web and a single opening therein and in which thehollow regions of the core portion communicate through constrictedpassages defined by the stiffening ribs;

FIG. 1B is a bottom view of a spinneret plate in accordance with thepresent invention for producing the straight-edged trilobal filament ofFIG. 1A;

FIG. 2A is a cross section view of a straight-edged trilobal filamentgenerally similar to that shown in FIG. 1A in which the stiffening ribsconnect with each other to isolate the hollow regions defined in thecore portion;

FIG. 2B is a bottom view of a spinneret plate in accordance with thepresent invention for producing the trilobal filament of FIG. 2A;

FIG. 3A and FIG. 4A are cross section views analogous to the views shownin FIGS. 1A and 2A, respectively, of straight-edged trilobal filamentsin which each lobe has a second transverse stiffening web and a secondopening therein;

FIG. 3B and FIG. 4B are bottom views of spinneret plates in accordancewith the present invention for producing the trilobal filaments of FIGS.3A and 4A, respectively;

FIG. 5A, FIG. 6A, FIG. 7A and FIG. 8A are each cross section viewsanalogous to the view shown in FIGS. 1A through 4A, respectively, oftrilobal filaments in which the lateral edges of each lobe are convexlycurved;

FIG. 5B through FIG. 8B are bottom views of spinneret plates inaccordance with the present invention for producing the trilobalfilaments of FIGS. 5A through 8A, respectively;

FIG. 9A and FIG. 10A are cross section views analogous to the viewsshown in FIGS. 1A and 2A, respectively, of tetralobal filaments in whicheach lobe has straight-edges and a single opening therein;

FIG. 9B and FIG. 10B are bottom views of spinneret plates in accordancewith the present invention for producing the tetralobal filaments ofFIGS. 9A and 10A, respectively;

FIG. 11A and FIG. 12A are cross section views analogous to the viewsshown in FIGS. 5A and 6A, respectively, of tetralobal filaments in whicheach lobe has convexly curved edges and a single opening therein;

FIG. 11B and FIG. 12B are bottom views of spinneret plates in accordancewith the present invention for producing the trilobal filaments of FIGS.11A and 12A, respectively;

FIG. 13A is a cross section view analogous to the view shown in FIG. 3Ashowing a tetralobal filament in which each lobe has straight edges withtwo openings therein, and in which the hollow regions of the coreportion communicate through constricted passages defined by thestiffening ribs;

FIG. 13B is a bottom view of a spinneret plate in accordance with thepresent invention for producing the straight-edged tetralobal filamentof FIG. 13A;

FIG. 14A is a cross section view analogous to the view shown in FIG. 8Ashowing a tetralobal filament in which each lobe has convexly curvededges with two openings therein, and in which the stiffening ribsconnect with each other to isolate the hollow regions defined in thecore portion; and

FIG. 14B is a bottom view of a spinneret plate in accordance with thepresent invention for producing the tetralobal filament having convexlycurved edges as shown in FIG. 14A.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the following detailed description similar reference numeralsrefer to similar elements in all Figures of the drawings.

Filament

FIG. 1A is a cross section view of a trilobal thermoplastic syntheticpolymer filament generally indicated by the reference character 10 inaccordance with the present invention. A filament in accordance with thepresent invention may be prepared using any synthetic, linear,thermoplastic melt-spinnable polymer, including polyamides, polyesters,and polyolefins. After melting the polymer is extruded (“spun”) througha spinneret plate (to be described hereinafter) under conditions whichvary depending upon the individual polymer and the particular filamentbeing spun thereby to produce a filament having a desired denier and adesired void percentage. Void percentage can be increased by a morerapid quenching and increasing the melt viscosity, which can slow theflow allowing sturdy, pronounced molding to occur.

The filament 10 shown in FIG. 1A has a central core portion 12 havingthree lobes 14A, 14B, and 14C joined thereto (i. e., the numberN=three). An axis 10A extends centrally and axially through the coreportion 12 of the filament 10. Each lobe 14A, 14B, 14C terminates in agenerally rounded tip 16A, 16B, 16C, respectively.

The tips 16A, 16B, 16C of each lobe 14A, 14B, 14C lie on acircumscribing circle 18 having a radius R₁ centered on the axis 10A.The junction between each lobe 14A, 14B, 14C and the core portion 12lies on an inscribing circle 22 having a radius R₂ centered on the axis10A. The modification ratio (i. e., the ratio of the radius R₁ to theradius R₂) of the filament 10 is in the range from about 1.6 to about4.0, more preferably in the range from about 2.0 to 3.0, and mostpreferably in the range from about 2.3 to about 2.6.

The major portion of each lateral edge 24A, 24B of each lobe 14A, 14B,14C is substantially linear to impart a substantially “straight”appearance over substantially the entire length between the tip 16A,16B, 16C and the joint of the respective lobe 14A, 14B 14C to the coreportion 12. The lateral edges 24A, 24B of each lobe 14A, 14B, 14Cconverge toward each other to define an arm angle 26 for each lobe 14A,14B, 14C. The arm angle 26 lies in the range from about zero to aboutfifteen (15°) degrees.

The core portion 12 has three stiffening ribs 30A, 30B, 30C formedtherein. The ribs 30A, 30B, 30C lie within the inscribing circle 22 andextend within the core portion 12 in a radially inward direction towardthe axis 10A of the filament. Each rib 30A, 30B, 30C has a respectiveinner end 32A, 32B, 32C thereon. The ribs 30A, 30B, 30C cooperate todefine three hollow regions 36A, 36B, 36C in the core portion 12. Thehollow regions 36A, 36B, 36C extend axially through the filament 10.Each hollow region 36A, 36B, 36C aligns radially (with respect to thecentral axis 10A) with a respective lobe 14A, 14B, 14C.

In accordance with the present invention each lobe 14A, 14B, 14C has atleast one opening 40A, 40B, 40C, respectively, therein. The opening 40A,40B, 40C in each respective lobe 14A, 14B, 14C is disposed between thelobe tip 16A, 16B, 16C and the inscribing circle 22. The openings 40A,40B, 40C also extend axially through the filament 10. The opening 40A,40B, 40C together with the hollow region 36A, 36B, 36C corresponding tothe lobe cooperate to define a transverse stiffening web 42A, 42B, 42Cextending across the lobe.

In the embodiment of the invention illustrated in FIG. 1A the radiallyinner ends 32A, 32B, 32C of adjacent stiffening ribs 30A, 30B, 30C arespaced from each other and from the central axis 10A of the filament 10.The spacing between the inner ends 32A, 32B, 32C of adjacent ribs 30A,30B, 30C defines passages 46A, 46B, 46C through which the hollow regions36A, 36B, 36C may communicate with each other. In the embodimentillustrated the transverse dimension of the passages 46 is relativelyconstricted with respect to the transverse dimension of the associatedhollow region 36, although such a relationship is not required.

In the embodiment shown in FIG. 1A the hollow regions 36A, 36B, 36C andthe passages 46A, 46B, 46C form a unitary void that extends centrallyand axially through the core portion 12 of the filament 10. Therelatively constricted shape of the passages 46A, 46B, 46C as comparedto the hollow regions 36A, 36B, 36C imparts a generally “clover-like” or“propeller-like” shape to the unitary void.

The presence of the openings 40A, 40B, 40C together with the unitarycentral axial void formed by the hollow regions 36A, 36B, 36C and thepassages 46A, 46B, 46C results in a filament 10 in which the crosssection has a total void percentage (herein also “void%”; i. e., thepercentage of “open space” on the interior of the filament) that lies inthe range from about seven (7%) to about thirty percent (30%). Morepreferably, the total void percentage lies in the range from abouttwelve (12%) to about twenty-two percent (22%). As will be demonstratedby the Examples following herein the filament 10 in accordance with thepresent invention embodies various structural compromises that result inacceptable performance as measured against all desirable performancecriteria. The modification ratio, arm angle and void percentagecooperate to impart high cover, low glitter and good soil hidingperformance to the filament 10. The stiffening web 42 in each lobe 14retards the collapse of the lobe due to high force loading, while theribs 30A, 30B, 30C in the core portion 12 form abutting members on theinterior of the filament that contact with each other under high faceloading to enhance the stiffness and load capacity of the filament. Thepresence of these structural features imparts good crush resistance tothe filament.

Spinneret Plate

FIG. 1B illustrates the bottom surface 50B of a portion of a spinneretplate 50 for producing the filament 10 depicted in FIG. 1A. As is knownin the art a spinneret plate 50 is a relatively massive member having anupper surface and the bottom surface 50B. The upper surface of thespinneret plate is provided with a recess (not shown) whereby connectionof the plate 50 to a source of polymer may be effected. Depending uponthe rheology of the polymer being used the lower margins of the recessmay be inclined to facilitate flow of polymer from the supply to thespinneret plate.

A capillary arrangement generally indicated by the reference character54 extends through the plate 50 from its recessed upper surface to thebottom surface 50B. As is seen in FIG. 1B the capillary arrangement 54is defined by a cluster of peripheral slots 56A, 56B, 56C centered abouta central point 58. Each peripheral slot 56A, 56B, 56C itself comprisesa pair of slot segments indicated generally by the characters 60, 62.Thus, the peripheral slot 56A includes paired slot segments 60A, 62A;the peripheral slot 56B includes paired slot segments 60B, 62B; whilethe peripheral slot 56C includes paired slot segments 60C, 62C.

Each slot segment 60 is joined to its paired slot segment 62 at ajunction point 64. A rib-forming slot 66 extends from each junctionpoint 64 toward the central point 58 of the cluster. Each slot segment60, 62 includes a generally linear portion 60L, 62L extending from thejunction point 64 toward a generally rounded free end 60R, 62R. Thisarrangement serves to form the lobes 14 having linear lateral edges withgenerally rounded tips. The radius of the rounded free ends 60R, 62R iscentered on an origin 68. Adjacent rounded ends 60R, 62R are spaced by agap 63.

Each slot segment 60, 62 in a peripheral slot 56A, 56B, 56C isconfrontationally disposed with respect to a slot segment forminganother peripheral slot. Thus, in FIG. 1B, the slot segment 60A includedin the peripheral slot 56A is confrontationally disposed with respect tothe slot segment 62C included in the peripheral slot 56C. The slotsegment 62A included in the peripheral slot 56A is confrontationallydisposed with respect to the slot segment 60B in the peripheral slot56B. Similarly, the slot segment 62B included in the peripheral slot 56Bis confrontationally disposed with respect to the slot segment 60Cincluded in the peripheral slot 56C.

The distance between the junction point 64 and the central point 58 ofthe cluster occupied by each rib-forming slot 66 determines whether theradially inner end 32A, 32B, 32C of respective stiffening ribs 30A, 30B,30C are joined together or are spaced from each other and from thecentral axis 10A of the filament 10 (as in FIG. 1A). In general, toinsure that the inner ends of the ribs join along the axis (and thusserve to isolate the hollow regions in the core portion from eachother), the rib-forming slots should extend at least two-thirds of thedistance between the junction point and the central point of thecluster. On the other hand, if the rib-forming slots extend less thanone-half of the distance between the junction point and the centralpoint of the cluster, then the inner ends of the ribs are spaced fromeach other and from the axis. If the rib-forming slots extend at leastone-half but less than two-thirds of the distance between the junctionpoint and the central point of the cluster, then the viscositydetermines whether the ribs will join together at the axis of thefilament.

Web-forming slots 70, 72 are provided on each peripheral slot segment60, 62, respectively The web-forming slot 70, 72 on any given slotsegment 60, 62 extends toward a corresponding web-forming slot 70, 72(as the case may be) provided on the slot segment 60, 62 with which thegiven slot segment is confrontationally disposed. The inside ends of theweb-forming slots 70, 72 are separated by a space 74.

On FIG. 1B (and on all of the other views of spinneret plates discussedherein) alphabetic reference characters are used to indicate thedimensions of various features of the spinneret plate 50 that formcongruent features of the filament 10 of FIG. 1A. In FIG. 1D thecharacter A refers to the distance from the center 58 of the cluster tothe origin 68 of the rounded free ends 60R, 62R of the segments 60, 62,while the character B is the dimension of the radius of these free ends60R, 62R. The character C represents the distance from the central point58 to the inner wall of each slot 70, 72. The character D represents thespacing between the inner ends of the slots 66. The character Erepresents the dimension of the gap 63, while the character F representsthe dimension of the space 74. The character G represents the width ofthe peripheral slots 56. The character H denotes the width of the slots66, 72.

Polymer extruded from the capillary arrangement 54 forms the filamentillustrated in FIG. 1A. The presence of the generally linear portions60L, 62L with generally rounded free ends 60R, 62R serves to form afilament 10 having lobes 14 with linear (“straight”) lateral edges 24and generally rounded tips 16. The spacing between the confronting innerends of the web-forming slots 70, 72 insures that the polymer merges tocomplete a web 42 traversing each lobe 14.

Polymer emerging from the slots 66 defines the ribs 32. In FIG. 1B, therib-forming slots 66 occupy less than one-half of the distance betweenthe junction point 64 and the central point 58 of the cluster, and theinner ends 32 of the stiffening ribs 30 are spaced from each other andfrom the axis and the hollow regions 36 communicate through the passages46.

Typical numerical values of the various dimensions indicated by thealphabetic reference characters on FIG. 1B are as follows:

A=0.033″, B=0.013″, C=0.021″, D=0.095″,

E=0.0038″, F=0.0040″, G=0.0022″, and H=0.0018″.

These dimensions are given all at an arm angle of zero degrees.

Each of the spinneret plates 50 shown herein may be fabricated using thelaser technique disclosed in U.S. Pat. No. 5,168,143, (Kobsa et al.,QP-4171-A), assigned to the assignee of the present invention.

A modified embodiment of the filament 10 is shown in FIG. 2A. Themodified filament 10 of FIG. 2A is identical with that of FIG. 1A inthat it exhibits straight lobes with rounded lobe ends. However, themodified filament 10 of FIG. 2A differs from the filament of FIG. 1A inthat the hollow regions 36 in the core portion 12 are totally isolatedfrom each other. As is the case with the filament of FIG. 1A the ribs 30in the core and the stiffening web 42 in each lobe 14 places sufficientmaterial between the hollow regions 36 and the openings 40 to retardcrushing of the filament in case of high face loading.

Typical numerical values of the various dimensions indicated by thealphabetic reference characters on FIG. 2B (at an arm angle of zerodegrees) are as follows:

A=0.033″, B=0.013″, C=0.021, D=0.066″,

E=00038″, F=0.0040″, G=0.0022″, and H=0.0018″.

Particular attention is invited to the magnitude of the dimension D, thedistance between the rib forming slots 66 and the center of the cluster58. In FIG. 1B the dimension D (0.095″) is greater than the dimension Din FIG. 2B (0.066″). The rib-forming slots 66 in the spinneret of FIG.2B extend toward the central point 58 for a distance greater thantwo-thirds the distance between the junction point 64 and the centralpoint 58 of the cluster. As a result the stiffening ribs 30 of thefilament of FIG. 2A join together to isolate the hollow regions 36 fromeach other. In FIG. 1B the rib-forming slots 66 extend less thanone-half the distance between the junction point 64 and the centralpoint 58 of the cluster, so that the ends of the ribs 30 in FIG. 1A arespaced from each other.

FIGS. 3A and 4A show still other modified embodiments of a filament 10having straight lobes with rounded ends shown as in FIGS. 1A and 2A.However, the filament of FIG. 3A and FIG. 4A differs from its respectivecounterparts in FIG. 1A and FIG. 2A by the presence of a second opening41 in each lobe 14. The second opening 41 is disposed between the firstopening 40 and the tip 16 of the lobe 14. In each lobe the first opening40 and the second opening 41 cooperate to define a second transversestiffening web 43. The filament of FIGS. 3A and 4A each have sufficientmaterial between the hollow regions 36 and the openings 40 to retardcrushing of the filament in case of high face loading.

FIGS. 3B and 4B show spinnerets 50 used to produce the congruentfilaments illustrated in FIGS. 3A, 4A, respectively. In FIGS. 3B and 4Beach slot segment 60, 62, respectively, includes a second web-formingslot 71, 73. The second web-forming slot is located on a slot segment60, 62 intermediate the first slot 70, 72 (as the case may be) and thefree end 60R, 62R. The reference character C1 in these FIGS. 3B, 4Brepresents the distance from the central point 58 to the inner wall ofeach second web-forming slot 71, 73.

Typical numerical values of the various dimensions on FIG. 3B (at an armangle of zero degrees) are as follows:

A=0.047″, B=0.013″, C=0.038″,

C1=0.021″, D=0.095″, E=0.0038″,

F=0.0040″, G=0.0022″, and H=0.0018″

For FIG. 4B, typical numerical values of the various dimensions (at anarm angle of 0 degree) are:

A=0.047″, B=0.013″, C=0.038″,

C1=0.021″, D=0.066″, E=0.0038″,

F=0.0040″, G=0.0022″, and H=0.0018″

However, similar to the situation with the spinnerets of FIGS. 1B and2B, the dimension D of the rib forming slot 66 is different in FIGS. 3Band 4B. In FIG. 3B the dimension D=0.095″, (the slots 66 extend lessthan one-half the distance between the junction point 64 and the centralpoint 58 of the cluster), thus forming a filament in which the ends ofthe ribs are spaced from each other (FIG. 3A). In the spinneret of FIG.4B, the dimension D=0.066″ (the slots 66 extend greater than two-thirdsthe distance between the junction point 64 and the central point 58 ofthe cluster), so that the inner ends of the ribs 30 contact each other(FIG. 4A).

The filaments 10 shown in FIGS. 5A, 6A, 7A and 8A correspond those ofFIGS. 1A and 4A, respectively, save for the configuration of the lobes14. The filaments of FIGS. 5A, 6A, 7A and 8A each exhibit lobes 14 withconvexly curved lateral edges 24 and nipple-shaped lobe ends 16. Eachslot segment has rounded portions in the vicinity of the junction point64 to define concave cusps 25 on the perimeter of the filament betweenadjacent lobes 14. In accordance with this invention all of thesefilaments have sufficient material between the lobes to avoid filamentcrushing under load.

The lobes 14 of the filaments of FIG. 5A and FIG. 6A each have a singlestiffening web 42. The core regions 36 in FIG. 5A communicate with eachother, while in FIG. 6A the core regions 36 are isolated. The lobes 14of the filaments of FIG. 7A and FIG. 8A each have a pair of stiffeningwebs 42, 43. The core regions 36 in FIG. 7A communicate with each other,while in FIG. 8A the core regions 36 are isolated.

FIGS. 5B and 6B illustrate a spinneret structures corresponding to thefilaments of FIGS. 5A and 6A. These spinneret structures are generallysimilar to those shown earlier except that the linear portions 60L, 62Lpresent in the spinnerets of FIGS. 1B through 4B are omitted. Each slotsegment 56 is defined by a rounded or arcuate portion 60R, 62R centeredon an origin 68 that corresponds to each of the convexly curved lateraledges of the lobes. Each lobe 14 thus exhibits a configurationreminiscent of a gothic arch. The arcuate portions 60R, 62R are joinedin the vicinity of the junction point 64 by a rounded transition region65 that defines the concave cusps. The reference character A stilldenotes the distance from the center 58 of the cluster to the origin 68,while the reference characters B and B1 respectively denote the radiusof the rounded portions 60R, 62R of the lobes and the radius of thetransition region 65. Only one of each such radius is shown for clarity.The transverse dimension of the rib forming slot 66 is given by thecharacter H, while the transverse dimension of the web forming slots 70,72 is given by the character H1.

Typical numerical values of the various dimensions indicated by thealphabetic reference characters on both FIG. 5B and FIG. 6B are asfollows:

A=0.028″, B=0.040″, B1=0.0085″,

C=0.020″, E=0.0038″, F=0.0040″,

G=0.0022″, H=0.0018″, H1=0.0016″,

In FIG. 5A the hollow regions 36 communicate with each other through thepassages 46 to impart “clover-like” shape to the unitary void in thecore. In FIG. 6A the hollow regions 36 are isolated from each other. Asdiscussed in conjunction with FIGS. 2B and 4B, to form such filaments itis necessary merely to modify the distance that the rib-forming slots 66extends toward the center 58, as denoted by the dimension D. In FIG. 5Bthe dimension D is 0.010″ and the slots 66 occupy less than one-half thedistance between the junction point 64 and the central point 58 of thecluster. In FIG. 6B the dimension D=0.0066″, and the slots 66 occupygreater than two-thirds the distance between the junction point 64 andthe central point 58 of the cluster.

Typical numerical values of the various dimensions indicated by thealphabetic reference characters on both FIG. 7B and FIG. 8B, are asfollows:

A=0.048″, B1=0.0085″, C=0.020″, C1=0.039″,

E=0.0038″, F=0.0040″, G=0.0022″,

H=0.0018″, H1=0.0016

In FIG. 7B the dimension D is 0.095″ and the slots 66 occupy less thanone-half the distance between the junction point 64 and the centralpoint 58 of the cluster, imparting a clover-like shape to the coreregion. In FIG. 8B the corresponding dimension D is 0.0066″ and theslots 66 extend for greater than two-thirds the distance between thejunction point 64 and the central point 58 of the cluster. The ribs 32(FIG. 8A) join each other.

FIGS. 1A through 8A illustrates the present invention as applied to atrilobal filament (i. e., the number N is three). However, the presentinvention may also be implemented in the form of a tetralobal filament(i. e., the number N is four) having four lobes 14A, 14B, 14C and 14D.The lobes may have either straight or convexly curved lateral edges,with either single or double stiffening webs in each lobe, and witheither communal or isolated hollow regions in the core. Variousembodiments of tetralobal filaments with a single opening in each lobeare shown in FIGS. 9A through 12A. FIGS. 13A and 14A illustratetetralobal filaments having a pair of openings disposed in each lobe.

FIGS. 9A and FIG. 10A show straight-edged tetralobal filaments withcommunicating and isolated hollow regions 36, analogous to the filamentsof FIGS. 1A and 2A, respectively. FIG. 11A and FIG. 12A show tetralobalfilaments in which each lobe has convexly curved edges, with eithercommunicating or isolated hollow regions 36, analogous to the filamentsof FIGS. 5A and 6A, respectively. In the filaments of FIGS. 11A and 12A,the convexly curved edges meet without the presence of the rounded cusp25 (FIGS. 7A, 8A).

FIGS. 9B, 10B, 11B, 12B respectively show spinnerets for forming thefilaments of FIGS. 9A, 10A, 11A, and 12A. Typical dimensions of thespinneret apertures of FIGS. 9B and 10B are respectively the same asthose for the spinnerets of FIGS. 1B and 2B. The dimensions of thespinneret apertures for FIG. 11B and FIG. 12B are respectively the sameas the dimensions of the spinnerets of FIG. 5B and FIG. 6B.

FIG. 13A illustrates a straight-edged tetralobal filament produced usinga spinneret such as that shown in FIG. 13B. The filament has a pair ofopenings 40, 41 and a pair of webs 42, 43 in each lobe 14 andcommunicating hollow regions 36 in the core. Typical numerical valuesfor the various features of the spinneret of FIG. 13B would correspondto those of FIG. 3B. To produce a straight-edged tetralobal filamentwith isolated hollow regions 36 in the core a spinneret sized and shapedanalogously to that shown in FIG. 4B may be used.

FIG. 14A illustrates a tetralobal filament having convexly curvedlateral edges. The filament has a pair of openings 40 in each lobe 14and isolated hollow regions 36 in the core. FIG. 14B illustrates aspinneret which may be used to produce this filament. Typical numericalvalues for the various features of the spinneret of FIG. 14B wouldcorrespond to those of FIG. 8B. A spinneret sized and shaped analogouslyto that shown in FIG. 7B may be used to produce a convexly curvedtetralobal filament with communicating hollow regions 36 in the core.

TESTING METHODS

Luster & Glitter—Yarn

Luster is a property related to the reflection or refraction of parallelor directional light by various interfaces of the fiber. Lower lustercorresponds to higher light scattering. Glitter is the property producedwhen light is reflected or refracted from an area of a fiber whichdistinguishes that area from its surroundings. It is usually describedas a “sparkling” of the fiber. Lower glitter results in a fiber having aluster more like the luster of natural fiber.

The luster and glitter measurements set forth herein (Table 1) for theComparative and the Example (inventive) yarn samples were obtained fromreflectance readings made using a conventional photogoniometer-basedluster measurement instrument. A fixed angle of incidence (45 degree)and varied angle of detection were used. Each yarn sample was wound inparallel on a 20 mm×100 mm card and its reflectance measured by theinstrument. The half-peak width (HPW) obtained from the recording chartof the instrument is a measure of luster, with a smaller HPW indicatinghigher luster. The results of this test are listed in Table 1 under theheading “HPW”.

The luster and glitter of the Example and Comparative yarn samples werealso determined using a subjective visual luster and glitter tests. Thesamples were irradiated using a high intensity light and viewed by sixobservers. The yarn sample with highest luster was rated with “5” andthe yarn sample with lowest luster rated “1” by each observer. Therating for highest luster therefore was 6×5=30. These ratings areindicated in Table 1 under the heading “Subjective Luster”. For glittera ranking was used, i. e. highest glitter=“1”, and lowest glitter=“5”.These ratings are indicated in Table 1 under the heading “Glitter”.

Luster & Glitter—Carpet

The luster and glitter measurements set forth herein for carpet sampleswere obtained from internal reflection readings. The percentage ofinternal reflection or degree of light scattering inside the fiber is ameasure for classifying luster, glitter, and soil hiding. The lower theluster, the lower the glitter and the better the soil hiding capabilityof the carpet. The “glycol test” was used for measuring the internalreflection of carpet yarns. The reflection from a standard velour, winchdyed #2038A disperse gray, was measured before and after immersion inglycol. In the presence of glycol, reflection from the fiber surfaces issuppressed because of refractive index similarity between glycol andnylon 6,6. The relative reduction of reflection proved to be areproducible and reliable measure for the percentage external reflectionof yarns. The internal refection is calculated subtracting the externalreflection from one hundred.

To obtain external reflection, a calorimeter Colorgloss, type of lightC/10o is used. The CIE-L* is a numerical value for lightness of a samplefrom 0-100 (zero=black, 100=white). L*1—value: lightness of the samplemeasured w/o glycol. L*2—value: lightness of the sample measured inglycol.${{Percentage}\quad {external}\quad {reflection}} = {\frac{{L*1} - {L*2}}{L*1} \times 100}$

The results of this test are reported in Table 2 under the heading“Internal Reflection”.

Glitter of two Test Example samples and two Comparative carpet sampleswhich were both irradiated by a high intensity light was also determinedsubjective-visually. A ranking system highest glitter=“1”, and lowestglitter=“4” was used. The results of this test are reported in Table 2under the heading “Glitter”.

Carpet Cover

Cover was determined subjectively by ranking the light transmittancethrough the carpet samples having only a primary backing. The lower thelight transmittance the higher the cover or bulk in carpet. The resultsof this test are reported in Table 2 under the heading “Cover”.

Carpet Soiling

Carpet soiling was measured using the “Tetrapod” of four currentlypopular test methods. These test methods are: (1) Soil hiding-dry; (2)Soil hiding-wet; (3) Soil repellency-dry; and (4) Soil repellency-wet.The results of the carpet soiling properties are reported below in Table3.

The Tetrapod tests consisted of a series of cylindrical drums each 20cm. in diameter and 20 cm long. Each drum was rotated about thecylindrical axis on four rollers. Inside the drum was placed a fourlegged “walker” having rubber “soles” on the end of each leg. The“walker” has a hole in the center into which dirt was placed and washeld in position by a sieve. The piece(s) of carpet (total area 19 cm×62cm) were held against the inside surface of the drum by metal clips. The“walker” was placed inside the drum and the whole rotated at 50 rpm.Over a period of about 10 minutes about three grams of soil fell throughthe sieve and was distributed evenly over the carpet.

Soil Hiding-Dry

This is the default “Tetrapod” Test and was the only soiling test incommon use. Each 19 cm×62 cm carpet sample was tested at a time. Thetests lasted 3 hours and 20 minutes (10,000 turns). After this time allthe soil has been ground into the carpet. Vacuuming does not alter thecarpet appearance so it is usually omitted. Each carpet sample wascompared visually against a control piece of carpet which has also beenin the drum for 10,000 turns but without dirt. The comparison was doneunder standard lighting conditions using a gray scale [DeutscheIndustrie Norm (hereafter “DIN”) 54002].

Results from at least three independent observers were averaged to givea “note” from 1 (dirty) to 5 (clean). Half and quarter “notes”gradations are possible, defining a total of twenty-one possibledifferent “notes”.

Soil Hiding-Wet

The principle difference in this test was that the carpet was sprayedwith 6 ml of water immediately before placing in the drum. The carpetmust be allowed to dry before visual comparison.

Soil Repellency-Dry

In the soil hiding tests the soil has no choice: it ends up in thecarpet. The purpose of the soil repellency tests is to give the soil achoice: between one of two carpets, or the vacuum cleaner.

Two different carpet samples, each 31 cm×19 cm, were placed in the drum.The test was run for 10 minutes (500 turns) by which time all the soilhas left the reservoir and was on or in the carpet. The carpet was thenvacuumed using a upright vacuum cleaner with rotating brush. The vacuumcleaner sold by Nilsfisk as “Nilfisk GS 21” was used. Each tested piecewas then compared with an untested piece of the same carpet, using the“note” method described above.

Soil Repellency-Wet

This is similar to the dry test. Each piece of carpet was sprayed withthree (3) ml of water immediately before testing. After testing, thesamples are allowed to dry overnight before vacuuming.

Carpet Wear

Carpet was measured using (1) the static loading test; (2) the Vettermandrum test; and (3) the Castor chair test.

Static Loading

Static loading was measured according to DIN 54316 using a chair legtest to determine the compression behavior of a carpet sample loaded twohours at a pressure of 2.2 kg/cm². After a sixty minutes decompressiontime the remaining compression depth was measured. Original and finalcarpet pile height gives a rating based on a formula according to DIN54316. The higher the rating number the better the performance.

Vetterman Drum

Testing the change of the carpet appearance under mechanical loading wasdone by fixing the carpet sample inside metal drum with an internaldiameter of seventy (70) cm according to DIN 54328. The drum was rotated22,000 revolutions, with the direction of rotation reversed every fiveminutes. Throughout the rotation a 7.6 kg heavy round steel hall fittedwith fourteen rubber studs rolled over the carpet. The judgment orclassification of the carpet appearance change is donesubjective-visually, with the higher the rating number the better theperformance.

Castor Chair

The suitability of a carpet for wear or loading by office roller chairswas tested by the Castor Chair according to DIN 54324. After 5000 and25,000 turns a subjective-visual classification of the appearance changeof the carpet pile takes place according to DIN 54328. The higher therating number the better the performance of the carpet.

The results of the carpet wear properties are reported below in Table 4.

EXAMPLES

Three embodiments of nylon 6,6 bulked continuous filament (“BCF”) yarnin accordance with the present invention (“Test Examples”) were producedand compared with two prior art nylon 6,6 bulked continuous filamentyarns (“Comparative Examples”) having a solid trilobal and a hollow,square cross-section, respectively. The nylon 6,6 polymer used for allof the yarns had a relative viscosity of 75-80 RV, and contained nodelustering additives other than TiO₂. Identical process conditions forspinning, drawing, and bulking were used for all yarns.

The example yarns in accordance with the present invention were thefollowing:

Test Example 1

A trilobal hollow filament yarn as illustrated in FIG. 2A havingsixty-four (64) filaments and 1360 dtex, produced using the spinneret ofFIG. 2B.

Test Example 2

A trilobal hollow filament yarn as illustrated in FIG. 1A havingsixty-four (64) filaments and 1360 dtex, produced using the spinneret ofFIG. 1B.

Test Example 3

A trilobal hollow filament yarn as illustrated in FIG. 6A havingsixty-four (64) filaments and 1360 dtex, produced using the spinneret ofFIG. 6B.

The comparison yarns were the following:

Comparison A

A trilobal, solid filament yarn having sixty-eight (68) filaments and1260 dtex such as the yarn sold by E. I. du Pont de Nemours and Companyas DuPont 1301-O bright solid trilobal having a modification ratio of2.6.

Comparison B

A square hollow filament yarn having sixty-four (64) filaments and alinear density of 1360 dtex such as the yarn sold by E. I. du Pont deNemours and Company as Du Pont 1401-D bright square four-holecross-section having a percent hollow of 14.6 and a modification ratioof 1.4.

The optical properties of the yarns having a TiO₂ content of 0.02%(bright) were determined by the described methods for luster andglitter, and the results are reported below in Table 1.

TABLE 1 HPW Subjective Cand. MR Void % Luster Luster Glitter Comp. A 2.60 6.1 30 1 Comp. B 1.4 14.6 7.8 24 2 Test Ex. 1 2.6 14.3 9.3 12 4 TestEx. 2 2.6 15.7 9.9 7 5 Test Ex. 3 2.6 11.5 9.0 17 3

Carpet: In order to illustrate the invention concerning optical-,cover/bulk-, mechanical-, and soiling-properties velour carpets of theBCF-yarns with following carpet constructions were made and tested:68-77 stiches/10 cm, {fraction (1/10)} inch gauge, 570 g/m2 pile weight,6 mm pile height. Then #2038A disperse gray, latex and “ActionBac”backing for appearance retention, #9719 acid beige, latex for soiling.

The results of the optical and cover/bulk properties are reported belowin Table 2.

TABLE 2 Internal Glitter Cover Reflec- 1 = 1 = Cand. MR Void % tion HighHigh Comp. A 2.6 0 10.4% 1 4 Comp. B 1.4 14.6 53.0 2 3 Test Ex. 1 2.614.3 53.5 3 2 Test Ex. 2 2.6 15.7 58.5 4 1

TABLE 3 Tetrapod Soiling Dry/ Wet/ Cand. MR Void % TiO₂% Dry Cleaned WetCleaned Comp. A 2.6 0 0.02 3.50 3.75 1.50 2.25 Comp. B 1.4 14.6 0.023.50 4.00 2.25 3.00 Test Ex. 1 2.60 14.3 0.02 3.25 3.75 2.00 2.75 TestEx. 2 2.60 15.7 0.02 3.50 4.00 1.75 2.50

TABLE 4 Static Vetterman Castor Cand. MR Void % Ti0₂% Loading Drum ChairComp. A 2.6 0 0.02 3.6 2.0 2.3 Comp. B 1.4 14.6 0.02 3.6 2.5 2.6 TestEx. 1 2.6 14.3 0.02 3.8 2.0 2.6 Test Ex. 2 2.6 15.7 0.02 3.5 2.0 2.4

RESULTS

The yarn and carpet results shown in Tables 1-4 reveals a significantglitter/luster reduction and improvement in cover of the invented hollowtrilobal as against prior art solid trilobal and hollow squarecross-section filament or fiber products. Carpet wear and soilingperformance of the new hollow trilobal fibers are also better than solidtrilobal fibers.

From the foregoing it may be appreciated that the present invention isdirected to multi-lobal filaments that reflect light diffusely,resulting in low glitter. Filaments of the present invention exhibitgood soil hiding and covering ability without sacrificing crushresistance and without increasing the volume of the polymer material inthe fiber. The invention allows the use of less polymeric material,since the void content is higher than in conventional hollow filaments.This results in less material to be processed, disposed of and/orrecycled. Such filaments are very suitable for carpets and other textileproducts which are desired to exhibit high cover, good soiling anddurability performance, and natural glitter-free lusters. When used inapparel fabrics, the filaments of the invention provide good heatinsulation.

Those skilled in the art, having the teachings of the present inventionas hereinbefore set forth may effect numerous modifications thereto. Itshould be appreciated that such modifications are to be construed withinthe contemplation of the present invention, as defined by the appendedclaims.

What is claimed is:
 1. A thermoplastic filament having a central axistherethrough, the filament comprising: a core portion having N lobesjoined thereto, each lobe having a tip thereon, each lobe being joinedto the core portion along an inscribing circle, the core portion havingN stiffening ribs formed therein, the ribs extending radially inwardlytoward the axis of the filament, the ribs cooperating to define at leastN hollow regions in the core portion, each hollow region aligns radiallywith a respective lobe, each lobe having at least one opening therein,the opening in each lobe being disposed between the tip of the lobe andthe inscribing circle, the opening in each lobe and the hollow region ofthe core portion corresponding to that lobe cooperating to define atransverse stiffening web extending across the lobe.
 2. The filament ofclaim 1, wherein each stiffening rib has a radially inner end thereon,the radially inner ends of the ribs being spaced from each other andfrom the central axis of the filament thereby to define passages withinthe core portion through which the hollow region communicate with eachother.
 3. The filament of claim 1, wherein each stiffening rib isconnected to the other of the ribs along the axis of the filament,whereby the hollow regions are isolated from each other.
 4. The filamentof claim 1, wherein each lobe has at least a second opening therein, thesecond opening in each lobe being disposed between the first opening andthe tip of the lobe, the first and the second openings in each lobecooperating to define a second transverse web extending across the lobe.5. The filament of claim 3, wherein each lobe has at least a secondopening therein, the second opening in each lobe being disposed betweenthe first opening and the tip of the lobe, the first and the secondopenings in each lobe cooperating to define a second transverse webextending across the lobe.
 6. The filament of claim 2, wherein each lobehas at least a second opening therein, the second opening in each lobebeing disposed between the first opening and the tip of the lobe, thefirst and the second openings in each lobe cooperating to define asecond transverse web extending across the lobe.
 7. The filament ofclaim 1, wherein each lobe has a first and a second lateral edge, themajor portion of each lateral edge being substantially linear oversubstantially its entire length.
 8. The filament of claim 1, whereineach lobe has a first and a second lateral edge, the major portion ofeach lateral edge is convexly curved over substantially its entirelength.